Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless network includes a number of base stations each radiating to define a respective coverage area in which mobile terminals such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a mobile terminal within coverage of the network may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other mobile terminals served by the base station.
Further, a cellular wireless network may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to mobile terminals defining a downlink or forward link and communications from the mobile terminals to the base stations defining an uplink or reverse link. Examples of existing air interface protocols include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Wireless Interoperability for Microwave Access (WiMAX), and Global System for Mobile Communications (GSM), among others. Each protocol may define its own procedures for registration of mobile terminals, initiation of communications, handover between coverage areas, and other functions related to air interface communication.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies or range of carrier frequencies. Further, each coverage area may define a number of channels or specific resources for carrying signals and information between the base station and mobile terminals. For instance, certain resources on the downlink may be reserved to carry a pilot or reference signal that mobile terminals may detect as an indication of coverage and may measure to evaluate coverage quality. Further, certain resources on the uplink may be reserved to carry access requests from mobile terminals seeking to gain access to the base station. And certain resources on the downlink may be reserved to carry control messaging such as paging messages and random access response messages from the base station. In addition, certain resources on the uplink and downlink may be set aside to carry bearer traffic (e.g., user communications) in a manner assigned or scheduled by the station for instance.
When a mobile terminal is within coverage of a base station, the mobile terminal may from time to time transmit to the base station an access request message. The purpose of such an access request message may depend on the air interface protocol and the circumstances. By way of example, a mobile terminal may transmit an access request as a request to gain initial access to communication with a base station, such as to transition from an idle state to a connected state for instance or to facilitate handover to the base station. As another example, a mobile terminal may transmit an access request as a response to a page message and/or as a request to establish a particular communication connection such as a call or data session. As still another example, a mobile terminal may transmit an access request to register or reregister with a base station and/or to provide a location or tracking area update. And as still another example, a mobile terminal may transmit an access request to provide the base station with timing advance information or the like, to facilitate positioning. Once the base station receives a mobile terminal's access request, perhaps after further processing by the base station and/or associated infrastructure, the base station may then transmit an access response message to the mobile terminal.
By way of example, the initial access request that a mobile terminal transmits to the base station may take the form of a signature or pattern that is randomly selected from a plurality of signatures. For instance, in an LTE system, 64 signatures, referred to as preambles, are available, and the mobile terminal may randomly select one of the preambles to transmit to the base station. Since multiple mobile terminals may be transmitting access requests at the same time, the preamble may serve to differentiate the request transmitted by the mobile terminal from other requests originating from different mobile terminals. Once the base station receives the preamble, the base station may transmit an access response message corresponding to the received preamble. For instance, the response message may include an assignment of an initial uplink resource for the mobile terminal to use to communicate with the base station. In response to detecting the access response message corresponding to the preamble, the mobile terminal may then communicate with the base station on the assigned uplink resource to complete the communication connection.